Re: Dumper issue, revisited; invalid realloc/free

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 4 Feb 2015 14:37:32 -0500
> From: Rich Felker <dalias@libc.org>
> Cc: emacs-devel@gnu.org
> 
> > > http://www.openwall.com/lists/musl/2015/02/03/1
> > 
> > I suggest that you take a look at src/w32heap.c on Emacs's master
> > branch.  There' you will see a simple solution of a very similar (if
> > not identical) problem we have on MS-Windows.  It even includes a
> > simple handling of large allocations.
> 
> As I suspected, this code is used only if you use gmalloc.c. It's not
> used with system_malloc=yes, which is the case I'm concerned about.

No, you are mistaken.  The 'master' version of Emacs uses the system
malloc on MS-Windows.  Perhaps you are looking at the 'emacs-24'
branch, where indeed we use gmalloc.c and ralloc.c, with sbrk
emulation in w32heap.c.  But that's not what I had in mind.

> > Or that the libc memory allocation routines can gracefully handle
> > these situations.
> 
> I would not consider that "graceful". If they detect that the pointer
> passed to realloc or free is invalid, the only reasonable behavior is
> to abort.

They could do exactly what you planned to do: ignore the 'free' part
and only allocate a new block.